1. Field of the Invention
The invention herein relates to a kind of tire pressure alarm device that is of an uncomplicated structure, is not easily damaged and easy to assemble.
2. Description of the Related Art
Low tire pressure during vehicular travel is a frequent cause of automobile accidents and an alarm device that warns of insufficient tire pressure is urgently needed. As indicated in FIG. 1, previous tire pressure alarm devices had an insulative connector body (1) and a cap (2) mounted on the top, with a ring seal (10) installed between the connector body (1) and the cap (2), and positioned from top to bottom between the top section of the connector body (1) and the cap (2) were three circuit boards having surface mounted electronic components that formed the trigger device (31), and the power supply fixture (32) comprised of three batteries (321) installed in series, with a shell sleeve (322) constructed of an insulative material constitutig the exterior section of the batteries (321). An insertion hole (323) was drilled through the center of the shell sleeve (322) and installed at the insertion hole (323) by clipping, the trigger device (31) was mounted between the power supply fixture (32) and the spring (33) at the negative terminal at the topmost section of the batteries (321), and positioned at the bottom section of the shell sleeve (322) was a hollow recessed extension ring (34); the said extension ring (34) had an extension strip (341) that protruded upward and directly contacted the positive terminal of the said trigger device (31); inside the lower interior end of the connector body (1) was a brass threaded base (11) and the exterior section of the other end was covered by a metal protective shell (12), of which the hollow interior section of the threaded base (11) formed an air pressure chamber (111) for the induction of pressurized air, and the lower end had internal threads (112) that could be screwed onto the stem of a tire valve, and the said internal threads (112) were equipped with an oil seal (113) and a thrust rod (13) centered inside an air hole (131) such that the lower end of the thrust rod (13) was capable of pushing open the valve of the tire valve stem, thereby enabling air to pass into the air access hole (131) of the air pressure chamber (111) through the connector body (1), with the air pressure serving to produce the upward and downward movement of the flexible diaphragm (41) in the pressure switch (4) and, according to two presettable contact points, produce the continuity or non-continuity which determined whether the controlling trigger device (31) was provided with the electric current from the power supply fixture (32) required to invoke an audible signal. The said pressure switch (4) includes the diaphragm (41) that is mounted and sealed to the upper extent of the thrust rod (13) and the protrusion (411) at the center of the top section is capable of upward movement when pushed by air pressure; an active recessed seat (42) capable of upward and downward movement with the fixed confines of a guide ring (43), with the active recessed seat (42) having an upward facing opening and an outward projecting circular contact edge (421) and, furthermore, a hole (422) drilled at the center of the bottom section and the bottom surface against the protrusion (411) of the diaphragm (41); a coil spring (44) installed inside the active recessed seat (42); a hollow threaded base (45) that is positioned at a suitable interval at the upper extent of the active recessed seat (42) and has internal threads (451) along the interior and, furthermore, serrations (452) around the upper and lower circumference to prevent slippage; a conductive ring (46) fixed to the outer circumference of the active recessed seat (42), such that just before the active recessed seat (42) is supported by the top end of the diaphragm (41), the circular edge (421) contacts the inner edge along the top surface of the conductive ring (46) and, furthermore, the outer edge along the top surface of the conductive ring (46) is in solid contact with the relatively thin conductive extension ring (461), such that the pair of extension strips (462) projecting in an upward curve from the opposite sides of said extension ring (461) contacts the bottom surface of the extension ring (33) sleeved onto the lower end of the said shell sleeve (322) and thereby establishes continuity with the positive terminal of the power supply fixture (31) circuit and, furthermore, an adjustment screw (47), of which the external threads (472) of the head section (471) are screwed to the internal threads (451) of the hollow threaded base (45), and there is a shaft hole (473) through the center of the head section (471) as well as a slot (474) in the top surface to provide for the insertion of a screw driver, thereby enabling the upward and downward turning of the adjustment screw (47) to adjust the coil spring (44) that alters the pressure of the active recessed seat (42) exerted against the diaphragm (41).
Although conventional tire pressure alarm device are ideal in many respects, the said devices are quite difficult to utilize in actual application because: (1) Of the two different spaces formed in the upper and lower sections of the connector body (1), the active recessed seat (42), the coil spring (44), the hollow threaded base (45), the conductive ring (46), the extension ring (461) and the adjustment screw (47) are inserted into the upper space, while the diaphragm (41), the ring shell (43) and the threaded base (11) with the installed thrust rod (13) and the oil seal (113) are inserted into the lower space, a design that does not allow the insertion of all the components from a single end and which easily results in component droppage during assembly as well as other rather troublesome assembly difficulties. At the same time, since the degree of pressure sensitivity of the diaphragm (41), the ring shell (43) and the other pressure switch (4) components are of different design parameters, the pressure setting accuracy adjustments are often inconsistent and involves a lengthy testing period. (2) The seat area of the seal ring (10) in between the connector body (1) and the cap (2) is thin and fragile due to inadequate thickness and frequently breaks when impacted by rocks during the high speed rotation of the tire. (3) The enclosing of the connector body (1) in a metal protective shell (12) involves complex and difficult machine finishing and often leads to overall disassembly difficulties of the protective shell (12) and connector body (1).